Drayton Wiser and boiler cycling at low demand

[JasonClint]

Hi everyone, hoping there are some knowledgeable people here who can help me understand what's going on with my Wiser and boiler setup, and hopefully reassure me that it's not causing unnecessary wear and tear on my boiler...

Boiler is a Worcester Greenstar 30 CDi Classic Regular ErP and I have the Wiser 1 zone CH/HW kit.

Generally I find the system works well, and being able to heat individual rooms I am has I'm sure reduced our gas consumption.

The thing that's concerning me is how the system behaves when there is low demand for heat. I noticed this during the cold winter weather, where I had a room set to 12C (expecting the temp to really not get that low).

Overnight, the room thermostat was sitting right on 12C, and Wiser was responding to that by signalling low heat demand (their support have reviewed logs and confirmed demand was low at 20% - which in the Wiser system translates to switching boiler on for 2mins in every 10mins cycle). Their support have insisted that this is in line with industry-standard cycle times for gas boilers (i.e. 6 cycles in an hour - each cycle period 10 minutes).

I noticed, though, that because the call for heat was being switched off after only 2 minutes, my boiler didn't ever seem to be getting to the stage of actually firing up properly and adding heat to the system. From reading stuff, I think this is the 'pre-purge' stage of the boiler cycle? but I'm not an expert on boiler tech so would appreciate validation of this...

I could see from the water temp display on the boiler that by the end of the 2mins cycle, the temp hadn't risen at all - essentially the ambient temp water in the system had just been pumped around for 2 minutes. There was no noticeable heat added to the radiators or the room.

So my question is:

- Is this actually a problem? It feels like a boiler continuously cycling on for such a short time that it never reaches full firing stage is just a waste of energy, and must be putting unnecessary wear on things?

- Would it be better for the boiler to fire for 4 minutes every 20 minutes instead? This would at least add heat to the system, and allow the boiler to fully fire up. This is how Wiser cycles Oil systems (according to their support).

 

[Johntheo5]

Yes, that would be a better option IMO, 4 or 5 minutes every 20 minutes or so. Are you sure that the boiler is actually firing for those 2 minutes?, most gas boilers fire at ~ 60% of their max output and then modulate down to minimum but if the flow (boiler) temperature is set too low then the burner will cut at the SP+5C and go into anti cycle for a set period with the circ pump still running and then refire again, what boiler SP are you using?.

 

[JasonClint]

Thanks @Johntheo5 - what's SP?

This is what I'm observing....

Wiser starts calling for heating, boiler starts up, burner indicator is on. The heating circuit solenoid is open, and water is circulating around the radiators.



Then after 2 minutes, Wiser stops calling for heat (Heating light on Wiser control unit goes out) and the burner light on the boiler goes out.



As you can see, the water temp hasn't risen in the 2 minutes the burner light was on.

The boiler continues to 'operate' for another 2 or so minutes, I guess in some kind of post-cycle cooldown. The pump is still operating (the solenoid has closed on the heating circuit, so during this post-cycle phase the boiler is just pushing water around a short loop via a divert valve).

Then eventually everything goes quiet again!

Then ten minutes after the boiler initially kicked in, it all happens again.

I tested what would happen if I increased the demand for heat (by setting a room thermostat very high) - the first two minutes of the boiler starting up is identical, but then there is an audible change in the burner where it clearly ramps up the burner and the water temperature starts rising as you'd expect it to.

 

[ian1182]

You can tell the Wiser system you have an oil boiler to adjust the hourly cycle rate, it's just a setting option.

Have a look at this

Drayton Wiser and Vaillant Boiler

Hi I have a cpl of question, but I'm also posting as this might help others trying to get Drayton Wiser to work properly with Vaillant (or other boilers). Setup: ecotec plus 418, S plan, installing Drayton Wiser smart controls (currently 3 rad valves). Problem: the boiler is short-cycling...

www.diynot.com

I have used the oil option (on my gas boiler) for the past year or so and I'm sure it's helped. I now see 4-5 minute on followed by 15-16 minutes off whilst the system maintains a steady temperature.

Your comment about "The boiler continues to 'operate' for another 2 or so minutes", that's pump overrun to allow heat to disperse from the boiler. I think the normal time is about 5 minutes although it's an option which is set on the boiler itself

You can change the boiler type in the Wiser app via "settings" -> "devices" -> "Hub" -> "Heat Source Type"

However there is a problem with the current version of the app, it's rather reluctant to enter the "Heat Source Type" option. You may have to exit the app and try multiple time before it allows you to modify.

 

[Johntheo5]

Thanks @Johntheo5 - what's SP?

This is what I'm observing....

Wiser starts calling for heating, boiler starts up, burner indicator is on. The heating circuit solenoid is open, and water is circulating around the radiators.

View attachment 296490 View attachment 296491

Then after 2 minutes, Wiser stops calling for heat (Heating light on Wiser control unit goes out) and the burner light on the boiler goes out.

View attachment 296492

As you can see, the water temp hasn't risen in the 2 minutes the burner light was on.

The boiler continues to 'operate' for another 2 or so minutes, I guess in some kind of post-cycle cooldown. The pump is still operating (the solenoid has closed on the heating circuit, so during this post-cycle phase the boiler is just pushing water around a short loop via a divert valve).

Then eventually everything goes quiet again!

Then ten minutes after the boiler initially kicked in, it all happens again.

I tested what would happen if I increased the demand for heat (by setting a room thermostat very high) - the first two minutes of the boiler starting up is identical, but then there is an audible change in the burner where it clearly ramps up the burner and the water temperature starts rising as you'd expect it to.

SP is set point. It may not show that on your display when you turn the rotary dial but looking at the setting, probably ~ 60/65C.
If you mean the heating zone ("solenoid") valve has closed then this is not right IMO as this is controlled by a roomstat and should only close when the room temperature exceecs the roomstat SP (setpoint) temperature.

 

[JasonClint]

You can tell the Wiser system you have an oil boiler to adjust the hourly cycle rate, it's just a setting option.

Have a look at this

Drayton Wiser and Vaillant Boiler

Hi I have a cpl of question, but I'm also posting as this might help others trying to get Drayton Wiser to work properly with Vaillant (or other boilers). Setup: ecotec plus 418, S plan, installing Drayton Wiser smart controls (currently 3 rad valves). Problem: the boiler is short-cycling...

www.diynot.com

I have used the oil option (on my gas boiler) for the past year or so and I'm sure it's helped. I now see 4-5 minute on followed by 15-16 minutes off whilst the system maintains a steady temperature.

Your comment about "The boiler continues to 'operate' for another 2 or so minutes", that's pump overrun to allow heat to disperse from the boiler. I think the normal time is about 5 minutes although it's an option which is set on the boiler itself

You can change the boiler type in the Wiser app via "settings" -> "devices" -> "Hub" -> "Heat Source Type"

However there is a problem with the current version of the app, it's rather reluctant to enter the "Heat Source Type" option. You may have to exit the app and try multiple time before it allows you to modify.

Brill - this is exactly the conclusion I had come to, but Wiser support were very clear that they didn't recommend that and that they couldn't continue to support me with my issue if I were to use the oil setting... they wouldn't answer my question as to whether there were any other changes related to the Heat Source, or whether it simply affected cycle time.

But on the basis that you've done the same thing and it's worked for you - this is now what I'm going to do!

 

[JasonClint]

SP is set point. It may not show that on your display when you turn the rotary dial but looking at the setting, probably ~ 60/65C.
If you mean the heating zone ("solenoid") valve has closed then this is not right IMO as this is controlled by a roomstat and should only close when the room temperature exceecs the roomstat SP (setpoint) temperature.

Thanks. I think the Wiser unit is acting as the room thermostat in this instance, though, so essentially when the Wiser stops calling for heat that is the same as a room thermostat reaching temperature. So I think the solenoid closing is probably right in this case?

 

[Mister Banks]

It’s the hubr that calls for heat based on what the room or radiator thermostat is detecting the room temperature is. I think the hubr uses the information from the thermostats, mixes this info in with what it thinks are the room characteristics and then decides to fire the boiler or not.

 

[ian1182]

Brill - this is exactly the conclusion I had come to, but Wiser support were very clear that they didn't recommend that and that they couldn't continue to support me with my issue if I were to use the oil setting... they wouldn't answer my question as to whether there were any other changes related to the Heat Source, or whether it simply affected cycle time.

But on the basis that you've done the same thing and it's worked for you - this is now what I'm going to do!

Not sure of their concern. Whilst the Wiser system has many inbuilt smart features, it's "just" acting as an on/off switch to the boiler in respect of the CPH value. Unless you are using the opentherm module there is no management of the boiler by Wiser. It's can be undone in a jiffy if you find it makes no difference.

Whilst I may be wrong, all I believe the "Heat Source" value does (without opentherm) is to modify the cycle rate. 3 for an oil boiler, 6 for gas and 12 for electric.

 

[Johntheo5]

If the wiser heating demand is going on/off then presume this cycles the boiler on/off? which means the circ pump will stop, after pump overrun period and if its set to oil then the maximum cycles are 3 per hour but can be less than this?.

 

[JasonClint]

Not sure of their concern. Whilst the Wiser system has many inbuilt smart features, it's "just" acting as an on/off switch to the boiler in respect of the CPH value. Unless you are using the opentherm module there is no management of the boiler by Wiser. It's can be undone in a jiffy if you find it makes no difference.

I agree... I shall do it anyway!

 

[ian1182]

I agree... I shall do it anyway!

Your biggest problem may be to get the app to allow you to modify the Heat Source value

 

[ian1182]

If the wiser heating demand is going on/off then presume this cycles the boiler on/off? which means the circ pump will stop, after pump overrun period and if its set to oil then the maximum cycles are 3 per hour but can be less than this?.

The maximum number of cycles per hour is controlled by the specified boiler type. The Wiser app has 4 types (gas, oil, electric & Heat Pump). I don't believe there is a means to directly set the CPH value.

 

[Johntheo5]

If one selected oil and if the overrun/anticycle times are less than 16 minutes, say 10 minutes then is the CPH value 3?.

 

[ian1182]

If one selected oil and if the overrun/anticycle times are less than 16 minutes, say 10 minutes then is the CPH value 3?.

The Wiser Hub has no knowledge of the boiler pump overrun or anticycle settings. I'll caveat that with it may be different when the opentherm module is being used.